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4.1. Influence of a temperature cycling on a state of polarisation of crystals SBN

As it has been shown in item 1.1 chapter 3., in the course of a heating of crystals SBN it was observed change of polarisation in a blanket of fashions (a Fig. 3.6). More detailed information on polarisation evolution in a blanket has been gained by means of TSW a method.

Co-ordinate dependences pirokoeffitsienta acted in film in the course of a heating at temperature stabilisation, in the beginning on the one hand the sample, at a recurring heating - on the other hand.

In drawing 4.1 lateral views of co-ordinate dependences pirokoeffitsienta crystal SBN61 for different temperatures in the course of a heating are presented. Apparently from the presented lateral views of polarisation (the Fig. 4.1), after passage pirotokom the peak value, is observed polarisation evolution in volume of the sample. The central part completely depoljarizuetsja, and from both legs of crystal SBN61 polarisation is guided from a surface deep into the sample. Thus, the observable veering of polarisation in a warmed up stratum at samples SBN61 (a Fig. 3.6) is related, in difference from crystals DTGS, not with occurrence of a stratum with inverse polarisation [146], and with the full depolarisation of the central field and the subsequent indutsirovaniem in blankets of the sample of the polarisation guided from both legs from a surface deep into of the sample.

It is interesting to score, that the full depolarisation of sample SBN61 after cooling took place only if the crystal heated up to disappearance temperatures pirotoka.

Cooling of crystal SBN from lower temperatures leads to that polarisation from both legs of the sample is guided from depth to a surface. Corresponding co-ordinate dependence of an effective value pirokoeffitsienta is presented in drawing 4.2. The subzero value
pirokoeffitsienta corresponds to that field of the sample which polarisation is opposite to polarisation of the basic volume of a crystal, i.e. to a stratum with inverse polarisation. It is necessary to score, as in a blanket, and in the basic volume of the sample quantity pirokoeffitsienta is less, than at a polarised crystal (a Fig. 4.1 curve 1).

The net direction of polarisation after cooling (a Fig. 4.2) is opposite to the state of polarisation which is taking place around phase transition (a Fig. 4.1, a curve 4). Thus, the made experiments testify that after cooling from a paraelectric phase the sample of monocrystal SBN61 or completely depoljarizuetsja, or in it arises system of the colliding domains which net polarisation near to both surfaces is guided from depth to a surface.

Fig. 4.1. Co-ordinate dependences pirokoeffitsienta crystal SBN61. A curve 1 - right after polarisation (Т=300), 2 - Т=327 To, 3-T=335 To, 4 - Т=358 K.Strelkami accepts a direction of a vector of polarisation in the sample.

Fig. 4.2 Coordinate dependences pirokoeffitsienta crystal SBN61 after cooling from a paraelectric phase. By arrows the direction of a vector of polarisation in the sample is shown.

In chapter 3 it was scored, that at crystals SBN not possessing relaksornymi by properties, the polarisation state in samples after each cycle is reproduced.

In drawing 4.3 it is shown a lateral view of polarisation of sample SBN35 after polarisation to a heating (a curve 1) and after a heating (a curve 2). Thus, samples SBN35, unlike SBN61, maintain a polarised state. As crystal SBN61 possesses relaksornymi properties, and SBN35 is not present, it is possible to guess, what exactly they are the parent of an astable state of polarisation in these crystals.

Really, crystal SBN70 has polarisation allocation on a thickness of the sample (a Fig. 4.4) similar to the sample of crystal SBN61. As at a room temperature it is in a paraelectric phase (a Fig. 1.1) the inverse stratum in it is observed at a room temperature not only in the course of a heating from a ferroelectric phase, but also after polarisation at
To the given temperature (Rice 4.4 curve 1). When the given sample has been polarised at temperature ssgietoelsktricheskoj phases (About °s) character of allocation of polarisation in it corresponded to a lateral view of polarisation of samples with other concentrations of the strontium, being at a room temperature in a ferroelectric phase (a Fig. 4.5).

Fig. 4.3 Coordinate dependences pirokoeffitsienta crystal SBN35.

Curve 1 - right after polarisation, 2 - after a cycle a heating-cooling.

By arrow the direction of a vector of polarisation in the sample is shown.

As crystals SBN61 and SBN70 unlike crystals with smaller value «> possess relaksornymi properties, it is possible to guess, what exactly they are the parent of occurrence of an inverse stratum and an astable state of polarisation in these crystals.

For all explored samples value pirokoeffitsienta from the leg corresponding to the plus vector head of polarisation for 10-15 percent less than on an opposite side (a Fig. 4,4 and 4.5).

It is important to score, that the polarisation direction in an inverse stratum depends on what temperature action leads to its occurrence. So, in the course of a quasi-static heating, at the approach to temperature of phase transition polarisation from both legs of the sample is guided from a surface deep into the sample (a Fig. 4.1). After cooling from a paraelectric phase a polarisation direction in a stratum opposite - i.e. the polarisation vector is guided from depth to a surface (a Fig. 4.2).

Fig. 4.4 Coordinate dependences pirokoeffitsienta crystal SBN70. A curve 1 - the sample polarised at 25°С, 2 - polarised at 0°С. By arrows the direction of a vector of polarisation in the sample is shown.

Fig. 4.5 Coordinate dependences pirokoeffitsienta crystals SBN40 (a curve 1), SBN61 (a curve 2), SBN35 (a curve 3) and SBN50 (a curve 4). The polarisation direction in the sample is shown by an arrow.

Let's view the possible parent of distinction of a direction of polarisation in a blanket depending on character of temperature action. As the sample settled down on the copper holder (a Fig. 2.4), immediately placed in termostatiruemuju the cabinet (a Fig. 2.5), that, in the first case, in the course of a heating, in the sample exists a stationary lapse rate of temperature (a Fig. 4.6, and,), guided from the surface subjected to action of the modulated thermal stream, to the back leg. In case of action by the modulated thermal stream on the leg corresponding + Ps, a direction of a lapse rate of temperature to an opposite direction of polarisation existing in the sample (a Fig. 4.6,). At action of a thermal stream on the leg corresponding - Ps, the direction of a lapse rate of temperature coincides with a polarisation direction (a Fig. 4.6,).
The given distinction, most likely, also serves as the parent of that the stratum with inverse polarisation arises in the course of a heating only on the leg corresponding + Ps (a Fig. 3.2, 4.1 (a curve 4) and 4.4 (a curve 2)). That the given stratum is observed only at crystals SBN possessing relaksornymi by properties (i.e. at SBN61 and SBN70) confirms the deduction drawn earlier that relaksornye properties promote instability of a polarised state.

In the course of cooling the copper substrate donates heat quickly enough, and the peak temperature exists at centre of the sample, and the lapse rate from both legs is guided from a surface deep into (a Fig. 4.6,). Cooling is carried out from a paraelectric phase in which initially polarisation in the sample misses. In this case, as follows from experiment (a Fig. 4.2), a direction arising at transition through a Curie point of polarisation to lapse rate of temperature is opposite existing in the sample (a Fig. 4.6,).

Fig. 4.6. A direction of a lapse rate of temperature arising in the sample in the course of a heating (and,) and coolings ().

4.2.

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A source: Lisitsyn Vladimir Sergeevich. PYROELECTRIC PROPERTIES And the STATE of POLARIZATION of MONOCRYSTALS of FIRM SOLUTIONS NIOBATA of BARIUM of STRONTIUM And NIOBATA CALCIUM BARIUM. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2015. 2015

More on topic 4.1. Influence of a temperature cycling on a state of polarisation of crystals SBN:

  1. З.1. Temperature dependences pirotoka crystals SBN of a various composition
  2. influence of exterior actions on a state of polarisation of crystals CBN
  3. stabilisation of a state of polarisation of monocrystals SBN
  4. influence of impurities on physical properties of crystals SBN
  5. processes of switching of crystals SBN
  6. ferroelectric properties of crystals SBN
  7. domain structure of crystals SBN
  8. temperature dependences of residual polarisation
  9. crystalline structure of crystals SBN
  10. properties of crystals SBN
  11. optical properties of the uniaxial crystals paratellurita, iiobata lithium and SBN, as objects for examinations by a conoscopy method
  12. temperature Influence otzhiga on a phase state, a microstructure and a composition of thin films TSTS
  13. 3.3. Temperature dependences pirotoka crystals CBN of a various composition
  14. 2.2. The analysis of a state of polarisation in segnetoaktivnyh materials with use TSW of a method
  15. 1.4. Influence of spontaneous polarisation on properties of the interface stratums in a sheet ferroelectric material
  16. influence of an impurity to It on the dielectric hysteresis of crystals SBN61
  17. influence of impurities to It and Rh on pyroelectric properties of crystals SBN61